In the past decade there has been a growing need for Unmanned Underwater Vehicles (UUVs). This type of vehicle is typically used for scientific, photographic, and reconnaissance work. The UUV is typically a cylindrical shaped vessel with a rotor driven propulsor mounted at one end. The propulsor propels the vehicle to and from its work site. Airfoil-shaped control surfaces are used to direct the movement of the vehicle by deflection of the relative water flow across the contours of the control surfaces. These control surfaces are effective as long as the vehicle""s velocity is approximately two nautical miles per hour and faster. However, a UUV is often required to maneuver at speeds less than two nautical miles per hour. The vehicle may also be required to hover in position while being exposed to cross currents. Therefore, there are times the UUV""s control surfaces are ineffective and an alternate method of control must be sought.
One alternate is a tunnel thruster, which is a tunnel that houses a rotor or set of rotors. The rotor or rotors blow jets of water through the tunnel in the direction opposite to which the UUV is desired to be maneuvered. Most commercially available tunnel thrusters are used on yachts and other water craft. The tunnel thruster is mounted in a ship hull and used for short durations of time. The tunnel thruster is used for the purpose of maneuvering the water craft into position for docking. Thrust from the tunnel thruster is generated by one or two rotors mounted on a single shaft inside of the tunnel. Typically, power is provided by a hydraulic motor mounted outside the tunnel with torque being transmitted to the drive shaft by a set of bevel gears. The gears are housed in a strut which also supports the rotor shaft assembly. In some situations, a single rotor may be driven by a hydraulic motor which is mounted inside the tunnel on the same axis as the rotor. Hydraulic power to this motor is provided by hydraulic lines which are housed by a strut which supports the rotor/motor assembly. The strut is attached to the tunnel wall. These tunnel thrusters are sufficient for the applications which they are intended.
However, UUV operation usually requires a propulsion unit to be quiet, to be capable of sustained operation a high pressure due to the operating depth of a UUV. The following is true for most commercially available tunnel thrusters. The use of ball bearings and gears generates a great deal of mechanical noise, which is radiated by the structure surrounding it. The struts which support the drive shaft rotor assemblies or house the gears and hydraulic components create large wakes in the flow of water through the tunnels. These wakes are a noise source as the rotor blades tend to chop through them. The size of the struts also creates a large blockage in the flow area of the tunnel which lowers the efficiency of the assembly. The use of a single rotor or the use of two rotors turning in the same direction (both mounted at opposite ends of the same shaft) causes the flow of water leaving the tunnel to leave in a swirling motion. The seals used to seal the drive shafts and other components are not sufficient for the depth pressures required. In addition, the blade contours, surfaces finishes, and overall quality of the components would result in hydrodynamic noise and inefficiencies. In addition, because these systems employ the use of hydraulic motors, these assemblies also require the use of a pump, valves, reservoirs, and other hardware mounted outside of the tunnel. Current size of available tunnel thrusters do not provide for a very compact system for a vehicle which has limited space available. For these reasons listed above, commercially available tunnel thrusters are not a viable alternative for use in a UUV.
It is an object of the present invention to provide a tunnel thruster which is highly efficient, compact, and quiet.
It is another object of the present invention to provide a tunnel thruster which can operate at a depth pressure of at least 600 psi.
A tunnel thruster for a water craft which includes the following. A tunnel which fits into the water craft. A water tight motor housing having two ends, whereby the motor housing mounted in the tunnel. At least one strut attached between the tunnel and the motor housing to mount and secured the motor housing in the tunnel, where the at least one strut including a pathway for electric and instrumentation lines. Two electric motors each including a drive shaft extending from an end of the motor, the motors mounted in an inline position along a centerline of the tunnel inside the motor housing, such that the drive shafts of the motors extend from each end of the motor housing along the centerline. A water lubricated rotor duct assembly mounted on each end of the motor housing. The rotor duct assembly includes the following. A rotor attached to the drive shaft and about the motor housing, where the rotor having a main body which includes a front and a rear, and the front having a face. At least two blades extending from the main body of the rotor between the front and the rear of the main body of the rotor. A stabilizer shaft extending away from the motor housing, the stabilizer shaft extending from a center of the face of the front of the main body of the rotor, where the stabilizer shaft having a nose at an end of the stabilizer shaft which is forward of the face. A cavity milled in the rear of the main body of the rotor to receive the drive shaft, at least part of the motor drive housing, bearings and seals, such that the main body of the rotor is mounted over the motor housing and internally connected to the nose of the drive shaft. A rear seal assembly applying a seal against the drive shaft and against the cavity of the main body of the rotor. A rear journal bearing providing a bearing surface between the cavity of the main body of the rotor and the motor drive housing, where the rear journal positioned near the rear of the main body of the rotor, the rear journal bearing lubricated by water surrounding the rotor duct assembly. An inlet duct for attachment to the water craft to support the rotor duct assembly, where the inlet duct including an outer rim and a center hub centered in the outer rim, the outer rim for attachment to the water craft and for supporting the center hub, where the center hub for supporting the stabilizer shaft of the rotor, and where the center hub having a front and a rear, the rear of the center hub including a cavity milled to receive bearings. A forward bearing assembly in the cavity of the center hub, where the forward bearing assembly lubricated by water surrounding the rotor duct assembly. A thrust shoulder attached to the nose of the stabilizer shaft at the front of the center hub, the thrust shoulder having a front and a rear, where the rear of the thrust shoulder milled to receive the nose of the stabilizer shaft, where the thrust shoulder having a nose at the front of the thrust shoulder, and where the thrust shoulder aiding in retaining the forward bearing assembly in place. A forward seal assembly to receive the nose of the thrust shoulder. A duct cover which attaches to the front of the center hub and over the thrust shoulder, where the duct cover having a front and a rear, and where the rear of the duct cover including a cavity milled to receive the forward seal assembly and the thrust shoulder.